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Granite
A medium- to coarse-grained intrusive igneous rock composed of potassium-
and sodium-rich feldspar, quartz, minor plagioclase, and small amounts of
ferromagnesian minerals such as biotite or hornblende. It is the intrusive
equivalent of rhyolite.
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The photo on the left shows a reddish-orange, medium-grained granite
consisting of orange to pink feldspar, white plagioclase, grey quartz
with minor dark mafic minerals. The specimen is from southern Labrador.
The photo on the right shows a white, coarse-grained granite consisting
of white feldspar, grey quartz and black biotite; it contains an
inclusion of dark metamorphic rock. The specimen is from near Hare Bay,
Bonavista Bay.
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Diorite
A medium-grained intrusive igneous rock consisting mostly of andesine
plagioclase and pyroxene, and small amounts of hornblende and biotite.
It is the intrusive equivalent of andesite.
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The photo shows dark, medium-grained diorite containing black hornblende
and white plagioclase feldspar. The specimen is from the Gander River
area of central Newfoundland.
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Gabbro
A dark, medium- to coarse-grained intrusive igneous rock composed of
calcium plagioclase, pyroxene, and possibly olivine, but no quartz. It
is the intrusive equivalent of basalt and the deep intrusive equivalent
of diabase.
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Shown is a dark, coarse-grained gabbro consisting of black pyroxene
and/or hornblende and white plagioclase feldspar. The light-coloured
areas are rich in plagioclase and contain minor mafic (dark) minerals.
This specimen is from the Gander River area of central Newfoundland.
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Rhyolite Porphyry
Rhyolite is a very fine-grained to glassy extrusive igneous rock (i.e.,
volcanic), usually light in colour but not always, consisting
essentially of quartz (silica) and alkalic feldspar. It is the
extrusive equivalent of granite. A porphyry is an igneous rock of any
composition that contains conspicuous crystals (Phenocrysts) in a
fine-grained matrix.
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The photograph shows an outcrop of dark, fine-grained rhyolite
containing larger pink feldspar phenocrysts, which give a porphyritic
appearance. This example was photographed in the Swift Current area.
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Intrusion Breccia
A breccia is a rock consisting of angular fragments in a matrix of finer
particles. An intrusion breccia consists of older host rocks (wall rocks)
surrounded by younger intrusive igneous rocks.
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The photo shows black diabase or diorite brecciated and surrounded by
younger, intrusive, white granitic material. Specimen from the Hermitage
Peninsula, southern Newfoundland.
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Diabase Dykes (intrusive relationships)
A dyke is a sheet of intrusive rock that cuts across layering or bedding
in the surrounding rocks. Diabase is a dark-coloured intrusive rock,
found as dykes or sills, composed of mainly feldspar, pyroxene +/-
olivine. It is the intrusive equivalent of basalt and the shallow
intrusive equivalent of gabbro.
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The linear, black, diabase dyke shown cuts across (is intrusive into)
the layering/banding in older gneisses. The photo is from the Nain area
of Labrador.
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Granite with Vein
A vein is a thin sheet-like body of igneous rock or mineral(s) (e.g.,
quartz, barite) that precipitates (crystallizes) or intrudes into a
crevice or fracture in a rock.
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The white quartz veins in this photo cut across grey-weathering granite.
Quartz veins like this, located at Long Lake, central Newfoundland, are
a good place to look for gold.
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